Radio-frequency mixer



-changing means or Patented, Apr. 3, R1951 UNITED STATES PATENT OFFICE RADIO-FREQUENCY MiXR Robert H. Dicke, Cambridge, Mass., assignor, vby mesn'e assignments, to the United States ,of America as represented by the Secretary of War Application March 22, '1945s, Serial No. 584,226

1 Claim'. (Cl. -250-'5209 f This invention relates to electrical systems and more particularly to electricai systems 'in which the fifini'e's Of 'Various energies 'are 'combined lin novel combinations. According to conventional theory c'rtain ele'- linents, including vacuum tubes, silicon Acrystals and other devices possessing non-linear electrical characteristics, may be llsed as frequency changers These frequency changers are also ire'- Yferredto as mixers. When energy consisting fo'f ftwo'dilier'e'nt frequencies is impressed across such an 'element and a load, 'energy of several different frequencies `Will appear across the load. Includference of the two impressed frequencies'. In radio work this difference frequency lis often 'reifer'rejd to as the intermediate frequency. In norinal radio work the two'impressed frequencies come from a local oscillator and radio frequency signal source. In the case where very high gain 'receivers are used noise originating in the initial stages of the receiver is a matter of prime importance. Much of this noise may originate in the local oscillator. This is true when the energy from the local oscillator is of more than one frequency. Frequencies present other than the fundamental may combine with the fundamental in the mixerand therein produce undesired noise at 'the same intermediate 'frequency as would be produced by energy from the signal source and the local oscillator.

An object of 'this invention, therefore, -is to provide apparatus for combining two sources of energy'in a manner such that the intermediate vfrequency energy output does not have components due to the combination of energy of two frequencies, from one of the energy sources.

VIn accordance with the pres-ent invention there is provided a device having two y frequency mixers. There are two sources of radio frequency energy, one or both of which contains noise which it is desired to eliminate. One of the sources of radio frequency energy is coupled .to the frequency changing meansI or mixers so that energy from this source will arrive at the two inixers inl phase. The remaining radio frequency energy sourceis coupled to the two mixers so that energyfromthis source will arrive at the two mixers in 180 phase opposition. Two coupling means are provided for deriving the end product produced by the two sources of radio frequency energy and the frequency changing means.

For a better understanding of the invention, to-

' 'in-'connection with the accompanying drawings,

'and the Scope of the invention will be pointed out lfi the appended claim..

2 In the'drawings: Fig. 1 shows 'a block diagram of one embodiinent ofthe invention;

Fig. -2 fsho'ws an embodiment of the invention in a wave vguide circuit; kand Fig. 3 shows an 'embodiment of the invention in a coaxial line circuit.

Referring now fr'nore particularly to Fig'. -1-of the drawings, there is shown a vbalanced mixer. This mixer maybe a vacuum tube, crystal or other Ifrequency changing device. -A radiov frequency Vsignal source II is adapted to feed mixers I 2 and I3. The mixers I2 and I3 are fed from this radio frequency 'source II in 180 phase opposition as shown by the waveforms at I4 and I5. A local oscillator source I6 feeds the mixers I2 and 1:3 also, but in phase, "as illustrated by the waveforms vat 2| and 22. The mixers I2 and I3 will function equally well if the signal :source III feeds the mixers I2 and I3 in phase and the local source I6 feeds the mixers I2 and I3 in Y180 phase opposition. The mixers 'I2 Vand I3 have their outputs 'combined to feed an intermediate amplifier 23. This is the normal position of intermediate frequency amplifiers in systems of the type being described. The mixer I2 fed by energies from points I4 and 2I will produce intermediate freduency 'energy at 24 with the phase illustrated by waveform 25 or 26 depending upon the manner in which the mixer is connected to operate. Likewise mixer I3 will produce 'an output at 3i with the phase illustrated by waveform 32 or 33 depend-ing upon the manner in which the mixer is 'connected to operate. The intermediate fre- `d'uency energy outputs at 24 and 3I may be Ycombined directly, i. e. added, in a manner well known in the art when the mixers I2 and I3 are so connected 'that the phase relationship of their outputs are as indicated by 'waveforms 25 and 32. If the connections of both mixers` I2 and I3 are reversed so that the phase relationship of their outputs ar' shown by waveforms 26 and 33 the ouputs may also be combined directly. The intermediate frequency energy outputs at 24 and 3| may be combined in push-pull if the phase relationship between the two outputs is The 4condition for push-pull operation will be satisfied if the mixers 12 and I3 are 4connected 'so that the phase relationship of their outputs are "as represented by waveforms 25 and 33 or by 'waveforms 2S- and 32. Any undesired output, such as noise. Awhich appears at 2'4 and -3I but which is due to the Acombination of energy of two frequencies which originate solely in one "of the two *sources will be cancelled 'out when the outputs 24 and -3I are "combi-ned. When 'the mixer I2 is connected to produce an output having waveform 225 or 26 the incise output will have waveform IlI or I3 respectively." yWhen the mixer I-3 is connected 'to produce :an output lhaving waveform32or 33 the @standing waves in the guide 4|.

'mixers 45 and 46.

waveforms and 33 the associated noise waveforms l1 and 28 have a phase relationship such that in any push-pull system they will cancel each other. A similar statement holds if the phase relationships are as shown in waveforms 2B and A32.

Referring now more particularly to Fig. 2, there is shown an embodiment of the balanced mixer of Fig. 1 in a wave guide circuit. Radio frequency energy enters wave guide 4| from a source 42.

`This energy will strike the termination 43, which in the case shown is a short circuit, and standing waves illustrated by the dotted line marked 44 will be set up within the wave guide.

Frequency changing means or mixers 45 and 4E, preferably crystal mixers, are placed within the wave guide a manner well known in the art and are separated by an electrical distance equal to an odd number of electrical half-wavelengths. In Fig.

`2 the mixers 45 and 46 are separated by one-half wavelength. A tuning screw is inserted into lwave guide 4|, intermediate termination 43 and the mixer 45 for adjusting the position of the By means of the 'Screw the standing waves 44 may be adjusted so thatthey are maximum in the positions of the Energy from a local oscillator source at 5| feeds into wave guide 4| at 52 -such that it reaches mixers 45 and 46 in phase.

In Fig. 2 the two electrical distances from 52 to each of the mixers 4-5 and 45 are equal to onequarter wavelength. Energy of intermediate frequency is supplied by the apparatus shown in Fig. 2 at outputs 53 and 54. These outputs 53 and 54 may be combined in phase or in push-pull, as described in connection with the discussion 0f Fig. 1, depending upon the manner in which the mixers 45 and 46 are connected. 'Ihe outputs 53 Vand 54 are shown connected to an intermediate frequency amplifier 41. The operational details 'other than those which have been described are well known in the art. The discussion of noise v,cancellation relating to the apparatus shown in Fig. 1 also applies to the apparatus shown in Fig. 2. f

'63. In Fig. 3 line branches 52 and 63 are termi- -nated in short circuits 54 and 65 which set up standing waves in the line.

Other terminations could be used but present practices favor the termination illustrated. In some cases the position -of the termination may be adjustable by means of 'la plunger not shown so that the position of the 'standing waves may be shifted. Frequency changing means or mixers 66 and 1|, preferably crystal mixers, are placed within the coaxial lines v`52 and 63 in a manner well known inthe art and are positioned so that the energy from line 6| arrives at the two mixers in 180 phaseV opcos'tion. This is accomplished when-F131` exceeds Dzoyan I"odd number of electrical half wavelengths, Di'being the distance from mixer 56 to signal source channel 6| and D2 being the distance from mixer 1| to the signal source channel 6|. Energy from a local oscillator 15 is inserted in lines 62 and 63 by means of a probe 12 or other means well known in the art. The insertion is made in such a manner that energy from the local oscillator arrives at the tWo mixers 68 and 1i in phase. This is accomplished when D3, the distance from the mixer 66 to the probe 12, and D4, the distance from mixer 1| to the probe 12, are equal to each other or the difference between them is an integral number of wavelengths. Integral number is assumed to include zero. The apparatus shown in Fig. 3 will function equally well if the signal energy arrives at the mixer in phase'and the energy from the local source arrives atthe mixers in phase opposition. The intermediate frequency energy from the mixers 65 and 1 is supplied to outputs 13 and 14. The mixers 66 and 1| may be arranged in a manner described for Fig. 1 to have outputs 13 and 14 either in phase or in push-pull. The discussion of noise cancel.- lation given for Fig. 1 also applies to the apparatus'shown in Fig. 3.

While there has been described what is at present considered the preferred embodiments of the invention, it-is obvious to those skilled in the art that various changes and modifications may be made therein without departing from thefin- Vention, and,it is, therefore, aimed in the appended claim to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

A balanced mixer comprising a wave guide for maintaining standing waves of electromagnetic energy signals and having an input end and a short circuited end, means to impress a first frequency signal upon said input end, a pair of crystal frequency mixers disposed within said wave guide, said mixers having their inputs spaced an odd number of the first signal half wavelengths from each other whereby the first signal arrives at said inputs in phase opposition, means to adjust the position of the standing waves within said wave guide located at said short circuited end whereby said standing waves will be` a maximum at said mixer inputs, means to impress a second frequency signal at the midpoint between said mixer inputs whereby said second frequency signal arrives in the same phase at both said mixer inputs, lmeans to derive a difference frequency of said first and second frequency signals from the output of each of said frequency mixers, and means to combine the difference frequency outputs of said mixers to derive a resultant signal.

ROBERT H. DICKE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,211,003 Conklin Aug. 13, 1940 2,296,107 Kimball Sept. 15, 1942 2,382,693 Dallenbach et al. Aug. l4, 1945y 2,408,420 Ginzton Oct.1, 1946 2,410,122 Mercer Oct. 29, 1946 2,413,939 Benware Jan. '1, l1941 2,420,892 McClellan May. 20,1947 2,469,222 Atwood ,May 3;'1949 

